Generally, a Real-time Transport Protocol (RTP) packet is used for transmitting media data in order to transmit video/audio using an Internet Protocol (IP) network, and an RTP Control Protocol (RTCP) packet is used for secondarily cooperating with the RTP packet.
In particular, one of various important functions of the RTCP packet is providing media synchronization information. Since the video and the audio are different media, a media sampling rate for acquiring an access unit corresponding to a unit of RTP packetization is different from each other.
Accordingly, the video and the audio need to be transmitted using each different RTP session. Information used for synchronization in a header corresponds to a “time stamp” field, and a value is independently generated for each video/audio access unit based on the sampling rate of the video and the audio.
Since the video and the audio independently generate a “time stamp” value, synchronization between the video and the audio may not be performed using only “time stamp” information. Accordingly, time information to which a video stream and an audio stream may be commonly referred is required for providing synchronization between the video and the audio.
A method of providing common time information uses an RTCP Sender Report (SR) packet. A “Normal Play Time (NPT) time stamp” field provides the common time information to which the video and the audio are commonly referred, and an “RTP time stamp” field records an RTP time stamp of the video or the audio corresponding to an “NPT time stamp”.
Accordingly, each RTP time stamp value by which synchronization between the video and the audio is performed by a medium of the “NPT time stamp” may be estimated. Each RTCP session is generated for each of a video session and an audio session, and is transmitted to be within 5% of the total traffic. Each time the RTCP session is periodically transmitted, the RTP time stamp of each media corresponding to the NPT time stamp is recorded in the RTCP packet and is transmitted, thereby enabling a receiver to acquire the information required for synchronization.
As described above, since a legacy media synchronization method requires the “time stamp” information of the RTP packet and transmission of the RTCP SR packet periodically providing the NPT time stamp value, complexity or a processing process is complex.
In particular, when an amount of traffic of a network is excessive, a congestion problem of the network may worsen due to the RTCP SR packet transmission.